1. Field of the Invention
The invention relates to the construction of a vector, and more particularly to a miRNA expression vector for improving the fertility of animals.
2. Description of the Related Art
Inhibin (INH) can specifically inhibit the pituitary cells from synthesizing and secreting follicle-stimulating hormone (FSH), and thus affects the maturation and development of the ovarian follicle in the ovary. Inhibin includes an α-subunit and a β-subunit which are connected by disulfide bonds. Only when the α subunit and the β subunit are integrated in vivo, the inhibin shows the bioactivity.
Studies show there is a close relationship between the α-subunit of the inhibin and the reproductive performance of animals. Insert 1-32 segments of the α-subunit into the carboxyl terminal of HBsAg-S to yield a DNA vaccine of the inhibin. 40 sheep were vaccinated by the DNA vaccine and the twin percentage thereof was measured. The results showed that the vaccinated group had an obviously higher twin percentage (39.2%) than a control group (the twin percentage was 10%) (P<0.05). Thus, the specific immunization targeting the inhibin by using the DNA vaccine induces the development of more ovarian follicles, thereby improving the fertility. Other studies also show that through the active immunization against the inhibin, antibodies of the inhibin are induced in animals, the inhibition of the endogenous inhibin on the synthesis and release of the FSH is relieved, thereby improving the fertility of animals. However, the active immunization against the inhibin works only in parental generations, the character of high fertility cannot be passed on to filial generations, and thus it is not a long-term mechanism.
miRNA is between 21 and 25 nt in length, and is originated from processing an endogenous transcript precursor pri-miRNA which is between 70 and 90 nt in length and is capable of forming a hairpin structure. miRNA is highly conservative in evolution. The specific complementary base pairing between miRNA and mRNA can degrade the mRNA or inhibit the translation of the mRNA, so miRNA plays an important role in gene regulations. The constituted-in-vitro miRNA expression vector targeting specific genes can effectively inhibit the expression of corresponding genes. Lentivirus, with lower transfection permission (both dividing cells and nondividing cells can be transfected) and higher transfection efficiency, is widely used for the regulations of gene expression.